Regensburg 2004 – scientific programme

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DY: Dynamik und Statistische Physik

DY 11: Ferrofluids

DY 11.2: Talk

Monday, March 8, 2004, 10:45–11:00, H3

Structure and Viscosities of Ferrofluids in Stationary Shear Flow — •Patrick Ilg¹, Martin Kröger², and Siegfried Hess¹ — ¹Institut für Theoretische Physik, TU Berlin, Hardenbergstr. 36, 10623 Berlin — ²Institut für Polymere, ETH Zürich, Sonneggstr. 3,8092 Zürich

Thanks to their superparamagnetic properties, the viscosities of ferrofluids are influenced by external magnetic fields - the so-called magnetoviscous effect [1]. This effect opens various technical as well as medical applications. In order to better understand the relationship between microscopic structure and magnetoviscous properties, we consider ferrofluids subject to a stationary shear flow. The model systems under consideration are studied both, with the help of mean-field approximations [2,3], as well as with nonequilibrium many particle simulations. The dependence on the magnetic field of the mass diffusion, viscosities and normal stress differences, cluster sizes and structure factors are presented. It is found, that mean-field approximations lead to satisfactory results within their range of validity, but cannot be extrapolated straightforwardly. Additional comparisons of the simulation results with SANS and rheological experiments on ferrofluids give valuable information on the importance of magnetic field and shear flow dependent structure formation for the strength of the magnetoviscous effect.

[1] M. Kröger, P. Ilg, and S. Hess, J. Phys.: Condens. Matter 15 (2003) S1403-S1423. [2] P. Ilg, M. Kröger, S. Hess, and A. Yu. Zubarev, Phys. Rev. E 67 (2003) 061401. [3] P. Ilg and S. Hess, to appear in Z. Naturforsch. 2003.